I don't do online dating, but I talk on online forums (obviously) and chatrooms, and that's how I met both the boyfriends I've had.

In comparison, every man I've asked out in person has said no, both before I was aware of polyamory and afterwards.

My experience isn't typical, though. As far as I understand, most people have more success dating in person than online, whether they are mono or poly.
I think I just work in a very... unusual way, which makes it harder to find compatible partners.